Radial burning in-situ combustion process utilizing a single well



, J. H. HENDERSON ETAL RADIAL BURNING IN-SIT 3,195,632 U coMBUs'rIoN-Haoc'sss UTILIZING A SINGLE WELL July 20, 1965 Filed June 17, 195'? INVENTORS United States Patent O RADlAl, BURNENG lN-SlTU CDB/EBUSTIUN PRGCESS U'lLlZ-NG A SNGLE WELL Eames H. Henderson, Gibsonia, and Malcolm R. J. Wylle,

Allison Park, Pa., assignors te Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Filed fune 17, 1957, Ser. No. 665,155 l Claim. (Cl. in-39) This invention relates to a process for the recovery of oil from oil bearing formations. lt is more particularly concerned with the secondary recovery of oil by an insitu combustion process employing a single well.

The primary recovery of oil from oil bearing formations, hereinafter referred to as pay Zones, utilize-s the natural pressure on the pay zone to force the oil through the permeable formation ofthe pay zone -to the well. The pressure on the pay Zone may be suicient to deliver oil to the well head or, if the pressu-re is not adequate, a lift is used to raise oil in the borehole to the surface. Usually only a small fraction of the oil present in the oil bearing formation can be recovered by primary recovery processes. Secondary recovery methods in which the pay zone is -repressured to move the oil through the formation are frequently used to increase the amount of oil recovered. The repressuring can be accomplished by the injection of gas into lthe upper part of the forma tion or water into the lower part to provide the drive required. ln another secondary recovery process referred to as an in-situ combustion process, oil in the formation is ignited and an oxygen-containing gas is pumped into the formation at an input well to continue the burning. The oxygen-containing gas and products of combustion force oil through the pay zone adjacent production well from which the oil is withdrawn.

This invention resides in an irl-situ combustion process employing a single well for the production of oil from a pay zone in which the pay zone is fractured and the fracture sealed with an impermeable material to form a barrier extending radially from the well. An oxygen-containing gas is injected into the pay zone above the barrier. Oil in the pay zone is ignited above the barrier and the injection of the oxygen-containing gas continued to force oil radially outward through the pay zone Varound the barrier and the-n radially inward to the well below the barrier. ln an embodiment of this invention which is particularly advantageous the pay zone is extensively fractured below the barrier, thereby facilitating ilow from the pay zone into the well.

The single figure of the drawing is a diagrammaticl representation, partially in vertical section, of a well adapted for use in the in-situ combustion process of this invention. Y

Referring to the drawing, the borehole indicated generally by reference numeral lil of a well is drilled completely through a pay zone l2 to a total depth lll. Pay zone 12 lies between base rock 16 and an impermeable cap rock 1S. The ground surface is indicated in the drawing by reference numeral Ztl. Casing 22. is set substantially to total depth in the borehole l@ and cemented at 2d completely through the pay zone l2. Any desired arrangement, illustrated diagrammatically by a cap 26, can be used to close the upper end of the casing 22 at the well head. For most effective use of this invention, pay zone l2 should be of substantial thickness, for example more than about l5 feet, in order to provide sumcient room in the lower portion of the bed for two separate radially extending fractures.

The casing 22 is perforated at 2S at the central portion of the pay zone and the formation then fractured at Sil through the perforations 28. The fracture 3% can be 3,l95,632 Patented July 29, 1965 ICC made by conventional fracturing techniques such as the technique described in United States Letters Patent No. 2,642,142 of J. B. Clark issued lune l6, 1953. And impermeable heat resistant cement such as a high alumina cement is squeezed into fracture 30 to form a barrier 31 extending radially from the well. The elevation of the fracture Sil, and hence barrier 3l, in the pay zone may vary substantially and the term central portion used to describe the position of the fracture 3i) only means that the fracture is at an intermediate position between the upper level at which the oxygen-containing gas is injected into the formation and the lower level at which the oil from the formation is delivered into the well. The exact loca-tion of the barrier 31 will be influenced by several variables such as the characteristics of the pay zone and the extent Iof the radial fracture made at a level below the barrier 31. When the pay zone is fractured extensively below the barrier 3l, it will be desirable to locate the barrier near the bottom, for example in the lower one-third of the pay zone, to take advantage of gravity segregation and obtain a larger air sweep pattern.

Any plug of cement that may remain in the casing after squeezing cement into fracture 3l) is drilled ou-t and the casing Z2 is then perforated at 32 slightly above the bottorn of the pay zone l2 and below the perforations 28. After the casing is perforated at 32 the pay zone 12 is fractured at 34 through perforations 32.

Fracture 3ft is preferably located as near the bottom of the pay zone l2 -as possible to allow recovery of the oil in substantially the entire pay zone. It is preferred that -t-he fracture 3d will be within about one-quarter of the thickness of the pay Zone from the bottom of the pay zone. A propping agent such as a coarse sand is deposited in the fracture to hold the fracture open to form a channel of large capacity to carry the oil and products of combustion to the well. Because of the very high resistance to flow of a three-phase mixture of gaseous cornbustion products, condensed water, and oil, through a permeable formation having very small openings the large channels through the fracture greatly reduce the resistance to flow from the formation to lthe Well.

Barrier 3l extends for sutlicient distance from the borehole to allow combustion of oil in a major part, preferably substantially all, of the pay zone in the drainage area of the well. ln a pay Zone in which many wells have been drilled, the well spacing will inuence the ,radial extent of the barrier 3l. lt is preferred that barrier 31 have substantially the same, or only slightly smaller, radius as fracture 34. Ordinarily fracture 34 will extend for a minimum radius of about 50 feet to a maximum radius of about 600 feet, depending on the characteristics of the particular oil field.

A series of perforations 36 are made in the casing 22 and surrounding cement at intervals through the pay zone above the barrier formed at fracture 30 and perforations 28 for the injection of an oxygen-containing gas in the manner hereinafter described. A heat resistant packer 3x8 is then set in the casing 22 above the perforations 28 and below the perforations 36 to separate perforations 32 and 36. A tubing di) .is run from the well head through packer 38 to a position with its lower end adjacent perforations 32. Tubing 40 is insulated as in- -dicated at 42 above the packer 3S to protect the tubing from the high temperatures in the casing 22 during ignition of the oil.

An ignit-er 44, which may be of the type described in United States Letters Patent No. 2,668,592 of I. J. Piros et al., is run in the annular space 46 between the casing 22 and tubing itl to a position adjacent the perforations 36. Igniter 44 is mounted on the lower end of a pipe 48 through which an oxygen-containing gas such as air or air enriched with oxygen ordiluted with an inert gas is delivered. A fuel line 5? extends downwardly through the pipe 48 and opens at its lower enel adjacent the igniter 44. Electric energy for supplying a .spark at the igniter 44 is furnished through suitable lead line 52.

Pipe 48 is connected at the well head to a source of the oxygen-containing gas through a line 54. Additional oxygen-containing gas, if required, is supplied through a line 56 opening into the annulus 46. The upper end of fuel yline 50 is connected to a source of fuel, such as natural gas or gas from a separator at the lease?, not shown.

In the operation of the apparatus illustrated in the gure, a fuel supplied through line 50 and an Voxygen-containing gas supplied through the pipe 4S are mixed and the mixture is ignited by igniter 44. The hot products of combustion are forced through perforations 36 into the pay zone and heat the oil in the pay zone to a temperature sufficiently high to start its combustion. `Heat to ignite oil in the formation adjacent the perforations 36 .can be furnished by means of an electric heater instead of by burning a fuel, if desired. Oxygen-containing gas is supplied in excess of that required by the fuel through line 56 to supply the oxygen for burning oil in the formation. n

After combustion of oil in the pay zone 12 has commenced, the How of fuel is stopped and the ow of oxygencontaining gas continued. The hot products of combustion force oil in the pay zone 12 radially outward Vpast vthe outer edge of the barrier 31. The oil then moves generally radially inward as indicated by arrows 58 to fracture 34 and then radially inward to the well bore. Oil is-delivered from the bottom ofthe well through tube 40 ybylany suitable means such as a pump, not shown. Oil from the formation iiows inwardly into the area defined by the barrier and fracture in the directions indicated by arrows 60.

In a specific example of this invention a well is drilled to a total depth of 4,010 feet through a pay zone 35 feet thick.V The top f the pay zone is vat a depth of 3,970 feet. Seven inch casing is set in the well toa depth of 4,008 feet and -cemented through the pay zone. The casing is perforated at a depth of 3,994 feet and is fractured with a leasercrude oil containing 1 to 2 pounds of sand per gallon for an average radius of 70 feet. A heat resistant cement is squeezed through the perforations into the fracture and pressure is maintained until the cement sets .to form a barrier extending radially through the pay zone. `A cement plug inthe casing is drilled toY a depth of 4,007 feet `and the casing isY perforated at a total depth-of 4,003 feet. Lease oil containing 1 to 2 pounds of sand per gallon is used in fracturing the formation through the perforations at 4,003 feet. A fractureabout 85 feet in radius is made in the pay zone.

The casing is then perforated at intervals .between theV barrier 4and the top of the pay zone.

A heat resistant packer is set in the casing immediately above the barrier and tubing is run through the packer to a depth of 4,003 feet. Natural gas and air are introduced .into the annulus above the packer and ignited adjacent the series of perforations above the barrier t0 heat oil above the barrier adjacent the borehole to ignition 1 temperature. The rate of ow lof natural gas is `5,000

standard cubic feet per dayand lof air is 100,000 standrad cu-bic feet per day. The flow of air and natural gas is .continued until the temperature of theformation adjacent the casing is 1,000o F. The ow of natural gas-is stopped and the flow of air increased in 48 hours to a rate of V150,000 standard -cubic feet per day at a pressure of 2800 pounds'per square inch Agauge at the well head,

and then continued at that rate. Oil delivered through the bottom fracture is lifted through the tubing to the well head.

This invention provides an in-situ combustion process u utilizing a single well forincreasing the production of loil `from a pay zone. The process is particularly valuable iwhen used in fields where, because of well spacing or the sweep of the gases into the pay zone radi-ally outward from the edge of the barrier and thereby increases the volume of the pay zone affected by the process of this invention. In the embodiment of the invention in which the fracture is near the lower border of the pay zone and the barrierVV is close to the fracture, control ofV the characteristics of the fracture allows control of the resistance to iiow into the well. By suit-able location of the barrier and selection of the size of the fracture and propping agent, the fracture will be substantially full of oil from the surrounding pay zone and the oil is driven to the well With a minimum gas-oil ratio by the pressure of the cornbustion products.

Heat transfer through the barrier to the lower section of the pay zone reduces the resistance to iiow through the lower section of the pay zone by raising the temperature of both the oil `and the formation, and is especially advantageous inthe embodiment in which the barrier is very close to the fracture.. The large area of the cylinder or frustum of a cone outlined by the outer edges of thebarrier and fracture allows Va large total flow radially inward from `the pay zone to the fracture evenV though the pressure on the pay zone is low.

We claim: f

A process for producingoil from a pay zone utilizing a single well penetrating the pay zoneV comprising forniing a first substantially horizontal fracture in the pay zone, said first fracturev being in the bottom one-fourth of the pay zone and'extending at least 50 feet radially from the well through the pay zone, propping the first fracture open with solid particles, forming a second substantially. horizontalV fracture above the first fracture, said second fractureV extending substantially the same distance into the pay zone as the lirst fracture and beingv in the bottom one-third of the pay zone, displacing cement into the second fracture to form a substantially horizontal barrier above the rst fracture, .setting a packer in the well adjacent the barrier to' divide the well into an upper zone Yabove the packer and `a lower zone below the packer,

running tubing down the well and through the packer to providea conduit extending down the well to the lower zone; said tubing and the wall of the well definingran annulus .above the packer, injecting an oxygen-containing gas down the` annulus and into the pay zone immediately above .the barrier, igniting oil in the formation above the barrier, continuing the injection of the oxygen-containing gas to continue combustion of oil in the pay zone above A the 'barrier to sweep oil radially outward from the well above the barrier and into the iirst fracture, delivering oil'throughthefirst fracture radially inward to the well, and lifting oil'delivered into the well through the first fracture through the tubing string to the surface. i

References Cited by the Examiner UNrrnD srArns ParleursA Y ne. 23,733

BENJAlvfIN HERSH, Primary Examiner. BENJAMIN BENDETT, Examiner. 

